In a typical cellular wireless network, the area covered by the network is divided into a number of cells. Each cell is served by a base transceiver station which transmits signals to and receives signals from terminals located in the respective cell associated with a particular base transceiver station. The terminals may be mobile stations, which are able to move between cells.
Channel allocation involves the allocation of a channel to a particular connection. There is usually an up link channel from the mobile station to the base station and a down link channel from the base station to the mobile station. The channels can be defined by different frequencies, time slots and/or spreading codes. Channel allocation can for some types of call such as data calls also require the selection of the allocation period. In WCDMA the allocation period is the period in the radio network controller that the packet scheduler can change bit rates for packet users. Channel allocation is done in a distributed way in the current networks. In particular, it is the responsibility of the controller of a base station to control the resources of its own base stations. In the GSM (Global System for Mobile Communications) standard, a base station controller (BSC) is arranged to control channel allocation for a set of base stations.
In the proposed third generation system using CDMA (Code Division Multiple Access), a radio network controller (RNC) is arranged to control the channel allocation for its own base stations. In the CDMA system, the base station is sometimes referred to as Node B. However in this document the term base station will be used. The controllers in both the GSM and CDMA systems are arranged to control a number of base stations. However the number of base stations which are controlled are relatively small. Accordingly, with this approach the efficiency of any channel allocation is limited in that the co-ordination of the channel allocation is possible only within the controller's own limited area. This means that it is not possible to co-ordinate channel allocation between cells that are controlled by different controllers. This in turn means that implementation of features that are intended to limit the interference between channels in adjacent or nearby cells cannot be achieved as the cells may be controlled by different controllers.
The problems described previously will become more relevant in the future. In some of the newly designed network architectures, such as IP based radio access networks, the channel allocation functions are moved from the controllers, such as the radio network controller and the base station controller, to the base station itself. This is in order to allow the implementation of a more efficient real time (RT) allocation of a channel. However, this removes even the possibility of co-ordinating the allocation of channels by base stations controlled by the same controller.
The limitations of the radio controller boundaries also have particular relevance when a network operator owns more than one radio access system (for example a CDMA system and a GSM system) with a common coverage area. This is because it is not possible to co-ordinate the allocation of channels in the different systems to reduce interference. In addition to third generation systems such as CDMA, other systems such as Wireless LAN (local area network), IS-41 (a US version of CDMA), etc are being developed.